Hello Haskellers, I want to implement the negascout algorithm for the game I'm writing. Wikipedia gives the algorithm in imperative terms: http://en.wikipedia.org/wiki/Negascout I've tried to translate this into Haskell. I'm not sure if I'm going about it the right way, and if I am, if I've done it correctly. Any comments on my effort here, are welcome: module Move (negascout ) where {-# contract negascout Ok -> {depth | depth >= 0} -> Ok -> Ok -> Ok #-} negascout :: Node -> Int -> Int -> Int -> Int negascout node depth alpha beta = case depth == 0 || is_terminal node of True -> evaluate node False -> let child:rest = children node b = beta -- initial window is (-beta, -alpha) in negascout' child (depth-1) (- b) (- alpha) beta rest -- Implementation {-# contract negascout' Ok -> {depth | depth >= 0} -> Ok -> Ok -> Ok -> Ok -> Ok #-} negascout' :: Node -> Int -> Int -> Int -> Int -> [Node] -> Int negascout' node depth beta' alpha beta rest = let a = negate $ negascout child depth beta' alpha in case a > (- alpha) of True -> let alpha' = a in case alpha' >= beta of True -> alpha' -- beta cut-off False -> case alpha' >= (- beta') of -- null window failed high? True -> let alpha'' = negate $ negascout child depth (- beta) (- alpha') -- full re-search in case alpha'' >= beta of True -> alpha'' -- beta cut-off False -> case rest of [] -> alpha'' child':rest' -> let b' = alpha'' + 1 in negascout' child' depth (- b') alpha'' beta rest' False -> case rest of [] -> alpha' child':rest' -> let b' = alpha' + 1 in negascout' child' depth (- b') alpha' beta rest' False -> case rest of [] -> alpha child':rest' -> let b' = alpha + 1 in negascout' child' depth (- b') alpha beta rest' -- Colin Adams Preston Lancashire